1. Field of the Invention
The present invention relates to a common channel signaling network, and more particularly, to a method of processing congestion conditions of a user part of a message transfer part in a common channel signaling system No. 7 network.
2. Background of the Related Art
A common channel signaling (CCS) system is a signaling system in which a traffic line and a signaling line are managed separately to transmit a signal for a call through the signaling line. For purposes of example, a CCS system No. 7 (SS7) will be described as an exemplary CCS system.
FIG. 1 is a simplified diagram illustrating an example of the configuration of signaling points of a SS7 network. As shown in FIG. 1, the signaling points constituting the SS7 network are divided into signaling end points and signaling transfer points (STPs).
FIG. 2 is a simplified block diagram illustrating the protocol stack of each of the signaling points constituting the SS7 network.
The protocol stack includes a telephone user part (TUP) 1, an ISDN user part (ISUP) 3, a transaction capabilities part (TCP) 5, a signaling connection control part (SCCP) 7, and a message transfer part (MTP) 9.
The telephone user part (TUP) 1 is adapted to perform basic call processing to control a telephone call, control of an exchange connection of a call, etc. The ISDN user part (ISUP) 3 is adapted to perform functions necessary to provide a circuit switching service and an additional service in view of a preparation for a request of various kinds of services of an integrated services digital network (ISDN).
The transaction capabilities part (TCP) 5 is adapted to perform a control of an exchange function and functions of special centers (e.g., a database, a special equipment unit, an operation and maintenance center) irrespective of a line. The signaling connection control part (SCCP) 7 is adapted to provide a transmission capability of a variety of signals or data except a typical line corresponding control signal, etc. Finally, the message transfer part (MTP) 9 is adapted to perform a transfer of a signal message.
The telephone user part (TUP) 1, ISDN user part (ISUP) 3, and signaling connection control part (SCCP) 7 are user parts (UPs) of the message transfer part (MTP) 9, and the transaction capabilities part (TCP) 5 is a user part (UP) of the signaling connection control part (SCCP) 7.
When comparing the MTP 9 with a 7-layered reference model of the Open System Interconnection (OSI) defined by the International Standard Organization (ISO), the lowest level or MTP level 1 of the MTP 9 is equivalent to the first layer of the OSI reference model or the physical layer. MTP level 2 of the MTP 9 is equivalent to the second layer of the OSI reference model or the data link layer. MTP level 3 of the MTP 9 is equivalent to the third layer of the OSI reference model or the network layer.
A signaling point that functions only to transfer a signal must have a protocol stack of the SCCP 7 and the ISUP 3.
The transfer of signaling messages of the MTP 9 in the SS7 network will now be described with reference to FIGS. 1 and 2.
As shown in FIGS. 1 and 2, for example, when assuming that a signaling message is transferred from a MTP user part of a signaling point A to a MTP user part of a signaling point F, the MTP user part of signaling point A requests a transfer of a signaling message to the MTP. The MTP routes the signaling message to an adjacent signaling point (B or C) through an available signal link set. At this time, the adjacent signaling point (B or C) receives the signaling messages from signaling point A, and routes the received signaling message to signaling point F which is a final destination signaling point. In the meantime, signaling point F receives the signaling message from the signaling point (B or C) and transfers the received signaling message to a MTP user part of signaling point F when a corresponding MTP user thereof is available.
Next, a transfer operation of a signaling message from a MTP level to a MTP user part of each signaling point will be described hereinafter.
As shown in FIG. 3, the MTP of signaling point F receives a signaling message from an adjacent signaling point, and transfers the received signaling message to a signaling message discrimination unit 10. The signaling message discrimination unit 10, in turn, determines whether or not signaling point F is the final destination signaling point of the received signaling message. If it is determined that the destination signaling point of the received signaling message is signaling point F to which the signaling message discrimination unit 10 itself belongs, the signaling message discrimination unit 10 sends the received signaling message to a signaling message distribution unit 30 to transfer it to a corresponding MTP user part of signaling point F. On the other hand, if it is determined that the destination signaling point of the received signaling message is not signaling point F to which the signaling message discrimination unit 10 itself belongs, the signaling message discrimination unit 10 transfers the received signaling message to a signaling message routing unit 20 to route the message to a corresponding signaling point.
Meanwhile, if signaling point F is the destination signaling point of the received signaling message, the signaling message distribution unit 30 receives the signaling message from the signaling message discrimination unit 10, and checks only an existence and an activation state of the corresponding MTP user part of signaling point F when performing a signaling message distributing function to determine whether to transfer the received signaling message to the corresponding MTP user part.
The related art signaling message has various problems. For example, when distributing the signaling message, the signaling message distribution unit 20 does not manage congestion conditions of the corresponding MTP user part. Accordingly, when the corresponding MTP user part of the destination signaling point is congested, the MTP of the destination signaling point and MTP user parts of other signaling points cannot recognize that congestion has occurred in the corresponding MTP user part of the destination signaling point. Accordingly, a MTP user part of the originating destination signaling point continues to transfer the signaling message to the destination signaling point F. The MTP of the destination signaling point also continues to transfer the signaling message to the MTP user part of the destination signaling point, so that the congestion conditions of the corresponding MTP user part of the destination signaling point continue during a predetermined period of time, which results in a complete interruption of a specific service.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.